Solid wire and tubular wire co-exist in the marketplace since each type of wire has its own pros and cons.
Solid wire provides a cost advantage and a consistency and precision in diameter, core composition, deposition, helix, cast, wire placement, feedability, surface chemistry, arc characteristics, etc. However, solid wire costs are driven primarily by the green rod cost that is largely dependent on economies of scale, thereby making it difficult for manufacturers to produce custom solid wire in smaller lot sizes due to the sourcing barrier of steel billets raw material from steel mills.
Tubular wire, characterized by a conglomerated or blended powder in the core and a metal sheath surrounding the core, benefits from changing chemistry for smaller lot sizes. However, tubular wire is difficult to produce when the finished diameter is too small (e.g., 0.030″ or less). Work hardening from folding the thin sheath may require annealing. For out of position welding, synergic pulse waveform may need to be developed for its increased melt-off rate and metal transfer behavior. It may have variation in powder density, homogeneity, compactness, and sheath thickness and may trap air and moisture inside the wire. Thus it may not be as consistent as solid wire in metal transfer and other welding characteristics. Reduced columnar strength may present wire feeding challenges. Seamless tubular wire overcomes some issues of the seamed tubular wire such as uniform outer surfaces for copper plating and being orientationally insensitive to deformation from drive roll pressure. However, seamless wire is more costly to produce due to batch filling and high frequency welding of the seam and also due to the batch annealing operations required to mitigate the work hardening effect. One issue characteristic of tubular wire is that there is a ballooning phenomenon in which the molten metal at the end of the wire increases in size larger than the wire diameter and dangles chaotically under the wire before detachment. Known as globular transfer, presumably due to the expansion of trapped air, it creates instability, a less focused arc, and shallow penetration. Another issue is that the instantaneous melt-off rate may not be as uniform as solid wire because the compactness or density of the powder in the core of tubular wire is not as homogeneous as the integral metal core of the solid wire. A further issue is the non-uniform heating and melting of the solid sheath and powder core, where the outer sheath may melt first, sometimes asymmetrically, and where the core material (e.g., tungsten carbide) is left to be dropped into the weld pool un-melted in solid form and bounced off the pool surface without being absorbed into the pool. What is needed is a system and a method that can economically produce custom chemistry or composition wire in solid form or a customized form to combine the merits of both solid wire and tubular wire.